Deep drawing method and apparatus



Feb. 1-0, 1970 w. T. SAUNDERS 3,494,169 A DEEP DRAWINGMETHOD ANDAPEARA'I'US V Filed Jan. 21, 1966 2 Sheets-Sheet 1 gm gig) 5325 m R AZTRiNG,30 35 Rlms I FIX-E2? DIE A 3 i i Z y P mNERRmms P P H04 FIGS H a QQ A A E Q 32 36 30 32 as so 32 as INVENFOR WILLIAM T. SAUNDERS ATTORNEWFeb. 10, 1970 w, T. SAUNDERS 3,494,169

DEEP DRAWING METHOD AND APPARATUS Filed Jan. 21, 1966 2 Sheets-Sheet 2FIG? - mvmon WILLIAM T. SAUNDERS B ysw ATTORNEYS .United States Patent3,494,169 DEEP DRAWING METHOD AND APPARATUS William T. Saunders,Weirton, W. Va., assignor to National Steel Corporation, a corporationof Delaware Filed Jan. 21, 1966, Ser. No. 522,312

Int. Cl. BZld 22/22 US. Cl. 72350 11 Claims ABSTRACT OF THE DISCLOSUREThis invention is concerned with cold drawing methods and apparatus forforming container bodies from sheet metal.

In cold drawing of sheet metal, a flat blank is placed between a diecavity and a movable punch and the metal is formed into the desiredshape by moving the punch into the die cavity. Edges of the die cavityand punch are sufiiciently rounded to prevent cutting of the metal andthe spacing between the die cavity and the punch is sufiicient to allowfor the .full thickness gauge of the sheet metal blank so-thatsubstantially no reduction in thickness of themetal takes place in thedrawing operation. q

However during drawing the. metal is subjected to stresses tending todeform the metal other than desired. For example, the peripheraldimensions of a sheet metal blank are reduced during a drawingoperation. This places the metal under compression in a peripheraldirection. At the same time, the drawing action tends to stretch themetal in a radial direction. The peripheral compression tends to bucklethe metal forming wrinkles and the radial tension tends to tear themetal. In a shallow draw these stresses can be held within strengthlimits of the metal being drawn. But, where the depth of draw requiresthe periphery of a blank to be decreased about twenty-five percent, ormore, the prior art had no economically practicable solution to thesestress problems. With soft metals, buckling or stretching of the metalwas accepted. With steel, several drawing steps were required, oftencoupled with heat treatment or other special steps to avoid tearing ofthe metal.

The present invention makes possible a deep-drawing operation where theperipheral outline of the blank can be decreased forty percent and morein a single stroke without formation of wrinkles and without tearing ofthe metal. In addition a uniform-thickness-sidewall container body canbe drawn because the metal is under substantially uniform pressurethroughout the single stroke. The invention is applicable toconventional temper (TU) steel, full hard steel plate such as thatproposed for container sidewalls, tinplated or other metallic platedsteel, and softer metals such as aluminum and copper.

The accompanying drawings will be referred to for a more detailed andspecific description of the invention, including other unique featuresand advantages. In these drawings:

FIG. 1 is a cross sectional schematic view of die structure at the startof a drawing operation,

FIG. 2 is a cross sectional schematic View of the die structure of FIG.1 at an intermediate stage in a drawing operation,

FIG. 3 is a schematic cross sectional view of die structure embodyingthe invention at the start of a drawing stroke,

FIGS. 4 through 6 are schematic, cross sectional partial views of thedie structure of FIG. 3 at intermediate stages of a drawing stroke, and

FIG. 7 is a schematic diagram partially in cross section of apparatusembodying the invention.

In FIGURES 1 and 2 a sheet metal blank 12 is drawn over a fixed die 14using movable punch 16. Fixed die 14 has a cylindrical shape and movablepunch 16 is tubular. The movable punch 16 is moved into overlappingcoaxial relationship with fixed die 14 and the metal at peripheralportion 18 of metal blank 12 is drawn down the sides of the die 14.

Metal blank 12 is gripped between movable punch 16 and pressure pad 20which is tubular in configuration and is coaxial and overlapping withfixed die 14. Great force is needed to initiate a draw and, to avoidformation of wrinkles, edges of the metal blank must be held with aforce matching that of the drawing force. Pressure pad 20 is used forthis purpose and the upward pressure of pad 20 will prevent wrinkling ofthe metal during a shallow draw.

It will be noted in FIGURE 2 that the area of the metal blank 22 betweenmovable punch 16 and pressure pad 20 decreases as the blank is drawn.The high pressures required for the draw are more concentrated as thearea of metal between the movable punch and the pressure pad decreasesand tearing of the metal will result if a deep draw is attempted. Alsothe metal has a tendency to stretch unevenly under these high pressurescausing earing of the cup, that is, the open edge of the article formedwill be uneven and its sidewall will have varying lengths at differingpoints about the open edge periphery. When back pressures are relievedin order to avoid tearing the metal or reduce the earing problem,wrinkling of the metal around the sidewall of the cup will beencountered during a deep draw.

The present invention permits deep-drawing in a single stroke, providesfor substantially uniform pressures on the metal during the draw toavoid earing of the metal, and at the same time prevents wrinklingwithout tearing of the metal. For this purpose a plurality of pressurerings are used which successively contact the metal blank being drawn toprevent wrinkling of the metal during the drawing stroke and, aftercontact with the metal blank, each of the pressure rings opposes thepressure of the movable punch to help equalize the pressure on thediminishing area of the metal blank being drawn.

The starting position for the single-stroke drawing operation of thepresent invention is shown in FIGURE 3. Circular metal blank 24 ispositioned over a cylindrical fixed die 26 and gripped at its outerperiphery between movable punch 28 and outer ring 30. The pressure onouter ring 30 is parallel to the longitudinal axis of fixed die 26 andexerts a force opposite to the direction of movement of movable punch28.

Referring to FIGURE 4, as the movable punch 28 starts downwardly thediameter of sheet metal blank 24 is decreased. After start of thestroke, and before the peripheral portion of sheet metal blank 24 losescontact with outer ring 30, middle ring 32 comes into contact with thesheet metal blank. It will be noted that middle ring 32 independentlyexerts a force similar in direction to that of outer ring 30'. Also, asshown in FIG. 3, that its upward movement is determined by flangesurface 34 between middle ring 32 and inner ring 36. Similarly, flangesurface 35 determines the upward movement of outer most ring 30. Flangesurfaces 34, 35, and

flange surface 38 between inner ring 36 and fixed die 26, serve asinterconnecting means to determine the initial positioning of the otherring 30, middle ring 32 and inner ring 36. Initial contact of middlering 32 with the sheet metal blank 24 is selected so as to preventwrinkling of the sheet metal blank and to maintain a continuoussubstantially uniform back pressure on the blank.

As movable punch 28 continues downwardly in its stroke the sheet metalblank terminates contact with outer ring 30. Before loss of contacthowever, pressure on the metal blank is spread over a greater area bythe contact with the middle ring 32. After termination of Contact ofsheet metal blank 24 with outer ring 30, the ring moves into contactwith movable punch 28 and the upward force exerted by outer ring 30opposes the downward pressure of movable punch 28. This reduces thepressure on the reduced-area peripheral portion of sheet metal betweenmovable punch 28 and middle ring 32 and helps equalize the pressure ofthe sheet metal blank during the drawing stroke.

As shown in FIGURE 5, sheet metal blank 24 has been drawn so that aperipheral portion is in contact with middle ring 32. Inner ring 36 hascome into contact with the sheet metal blank to prevent wrinkling of themetal and distribute the pressure exerted by punch 29 as the blank isdrawn. Outer ring 30 opposes the downward force exerted by punch 28.

In FIGURE 6, the peripheral portion of blank 24 is being drawn betweeninner ring 36 and movable punch 28. Outer ring 30 and middle ring 32exert a force in opposition to the downward pressure of movable punch28.

The number of pressure rings, the spacing of the rings along thelongitudinal axis of the die structure, and the individual force exertedby the rings are selected to make the pressure on the metalsubstantially uniform as the blank is drawn and thereby produce auniform thickness sidewall. In general the deeper the draw, the greaterthe number of rings to be used. Also, the blank contact area of theseveral rings can be varied to help maintain uniform pressure on themetal.

The basic principles of the invention have been described in relation toa cylindrical die and movable punch of tubular configuration. However,those skilled in the art will readily visualize the application of theseprinciples to other configurations and to drawing structure in which aclosed-end cylindrical punch draws the sheet metal by being moved intocoaxial relationship with a hollow die cavity. In the latter embodiment,the pressure rings are mounted in coaxial relationship with thecylindrical punch and spaced along its longitudinal axis. The pressurerings move with the cylindrical punch and help take up draw pressure andprevent wrinkling of the metal as the diameter of the blank decreases.As in the illustrated embodiment, the outermost pressure ring willcontact the peripheral portion of the sheet metal blank first and theinnermost ring will contact the blank last.

With either the tubular punch or closed-end cylindrical punchembodiments, the automatically functioning features of the inventionwhich prevent wrinkling or tearing of the metal come into playindependently without resort to a coordinated-movement physical linkagebetween the movable punch member and the rings to control pressure onthe metal. These features of the invention permit drawing of a sheetmetal blank to form a container body or cup shaped article withoutsubstantially changing the gauge of the metal. While some stretching ofmetal is practically inevitable in a drawing operation it is emphasizedthat the teachings of the present invention do not rely on stretching ofmetal to form the desired shape.

Assembled apparatus for single-stroke cutting and drawing of a sheetmetal blank is shown schematically in FIG. 7. Drive means 44, which canbe conventional, drives punch 46. On the downward stroke of punch 46sheet metal 48 is blanked by cutting edges 52 and 54. The cut blankisthen gripped between punch 46 and pressure ring 56 as the punch movesinto coaxial relationship with fixed die 58. Pressure ring 56 issupported by a plurality of pins such as pins 60 and 62 on thrust pad64. Spring 66 is supported between the thrust pad 64 and washer 68. Stem70 is threaded at 72 and nut 74 fixes the position of washer 68. Theforce exerted by spring 66 on pressure ring 56 can be varied byadjusting the position of nut 74 along the stem 70'.

As the blank is drawn, contact is made with inner ring 76. This ring issupported by a plurality of pins such as pins 78 and 80 which rest onthrust pad 82. Spring 84 acts between thrust pad 82 and washer 86. Nut88 fixes the position of washer 86 and can be used to adjust the forceexerted by spring 84.

The pin support structures are used in the embodiment of FIG. 7 to giveaccess to the adjustment nuts. Cylindrical supports with access holes toadjustment nuts could be used as well.

Other yieldable compression means can be substituted for the springsshown in FIGURE 7 and shock absorber rubber pads can be used at thethrust pads and washers. While the spring action is preferred forsimplified automatic functioning it is understood that pneumatic orhydraulic compression means could readily be used.

It is to be understood that the springs shown in FIG. 7 are for purposesof illustration only and are not neces sarily in true size relationship.The size of the springs and length of stroke of individual rings areselected based on the depth of draw and the material being drawn. Withthe present disclosure of the principles of the invention, selection ofspring sizes or other compression means, the number of rings, blankcontact area of individual rings, and the stroke of individual ringswill be within the purview of one skilled in the art. It is also to beunderstood that other ring support arrangements, than shown in FIG. 7which avoid physical connection between the rings and the movable punch,can be resorted to without departing from the scope of the invention ascovered by the appended claims.

What is claimed is:

1. Apparatus for forming a sheet metal blank into a container body by asingle-stroke deep-drawing operation compnsmg die means including a diecavity, punch means, and

means for moving the punch means into coaxial relationship with the diecavity to form a container body having an endwall and sidewall from asheet metal blank, and

a plurality of coaxial pressure rings positioned to successively grip anouter peripheral portion of the sheet metal blank as the sheet metalblank is formed, each pressure ring being yieldably mounted and havingmeans for independently exerting a force opposite in direction tomovement of the punch means during a drawing stroke, the plurality ofpressure rings including at least an outer ring and an inner ringarranged to contact the sheet metal blank around its entire peripherywith the outer ring contacting the sheet metal blank prior to contact bythe inner ring during a drawing stroke.

2. Apparatus for cold forming a sheet metal blank of predeterminedthickness gauge into a container body with a wrinkle-free sidewall ofsubstantially uniform thickness by a single-stroke deep-drawingoperation comprising an elongated fixed die over which the sheet metalblank is to be formed, the fixed die having an endwall surface and asidewall surface spaced from the longitudinal axis of the fixed die,

movable punch means having a tubular configuration with internaldimensions permitting the punch to be moved into overlapping coaxialrelationship with the fixed die with spacing between the sidewall of thefixed die and the movable punch means being at least as great as sheetmetal thickness gauge,

a plurality of pressure rings including an outer ring and an inner ringpositioned in overlapping and coaxial relationship with each other andfixed die,

yieldable pressure means acting on the pressure rings tending to forcethe pressure rings along a path parallel to the longitudinal axis of thefixed die in a direction opposite to the direction of movement of themovable punch means when the movable punch means is being moved intooverlapping relationship with the fixed die, and

interlocking means for initial positioning of the pressure rings inspaced relationship along the longitudinal axis of the fixed die so thatthe outer ring contacts the sheet metal blank prior to contact by theinner ring as the movable punch means is moved into overlapping coaxialrelationship with the fixed die to form the container body.

3. The apparatus of claim 2 in which the fixed die has a cylindricalconfiguration and the sheet metal blank has a circular configuration.

4. The apparatus of claim 2 in which the plurality of pressure rings arespring mounted to exert a force opposite to the direction of movement ofthe movable punch.

5. The apparatus of claim 2 further including blanking means for cuttingthe sheet metal blank as part of the single stroke operation prior todrawing of the sheet metal blank.

6. Method of forming a sheet metal blank into a container body by asingle-stroke, deep-drawing operation comprising the steps ofpositioning a sheet metal blank between a die cavity and a movable punchmeans,

driving the movable punch means under predetermined pressure into thedie cavity to shape the sheet metal blank into a container body havingan endwall surface and a sidewall surface, and during shaping of thesheet metal blank,

gripping a portion of the sheet metal blank about its entire peripherywith an individual pressure ring selected from a plurality of pressurerings yieldablymounted to independently exert a force against the sheetmetal blank in a direction parallel to direction of movement of thepunch means, the plurality of pressure rings including at least an outerring and an inner ring in coaxial relationship and positioned tosuccessively contact the sheet metal blank as the movable punch means isdriven into the die cavity with the outer pressure ring contacting thesheet metal blank prior to contact by the inner pressure ring.

7. In forming a container body from a sheet metal blank by single-strokedeep-drawing of the sheet metal blank by moving a tubular punch intooverlapping coaxial relationship with an elongated fixed die, a methodfor providing substantially uniform sidewall draw and preventingbuckling of sidewall metal of the container body during drawingcomprising the steps of providing a plurality of pressure rings oftubular configuration and positioned in overlapping coaxial relationshipwith each other and the elongated fixed die, the plurality of pressurerings including at least an outer pressure ring and an inner pressurering,

yieldably forcing the pressure rings in a direction opposite tothe'direction of movement of the tubular punch during a drawing stroke,

positioning the rings initially in spaced relationship longitudinally ofthe elongated fixed die to contact the sheet metal blank at diiferingtimes during a drawing stroke, with the outer pressure ring contactingthe sheet metal blank prior to contact by the mner pressure ring,

gripping the sheet metal blank between the tubular punch and the outerring, and

driving the tubular punch with predetermined force into overlappingrelationship with the fixed die so as to form the sidewall of thecontainer body, with a portion of the sheet metal blank around itsentire periphery coming into successive contact with individual pressurerings starting with the outer pressure ring, with each next adjacentinner pressure ring contacting the sheet metal blank before release byeach next adjacent outer pressure ring in order to apply continuouspressure on the sheet metal blank during drawing to prevent buckling ofthe blank and with each pressure ring opposing the force of the movablepunch after releasing the sheet metal blank.

8. In forming a container body by deepdrawing sheet metal over anelongated fixed die in a single stroke with a tubular punch which ismoved into overlapping coaxial relationship with the fixed die, a methodfor providing uniform sidewall draw and preventing buckling of sidewallmetal comprising the steps of providing a plurality of pressure ringsincluding an outer ring and an inner ring in coaxial and overlappingrelationship with each other and the fixed die, each pressure ring beingyieldably mounted to exert a force in a direction parallel to thelongitudinal axis of the fixed die and opposite to the direction ofmovement of the tubular punch when being moved into coaxial relationshipwith the fixed die, the plurality of pressure rings being positionedinitially along the longitudinal axis of the fixed die so that the outerpressure ring contacts the sheet metal prior to contact by the innerring during movement of the tubular punch into coaxial relationship withthe fixed die and driving the tubular punch under predetermined pressureinto overlapping relationship with the fixed die to form a containerbody.

9. The method of claim 8 further including the step of cutting a blankof predetermined peripheral dimension from the sheet metal during thesingle stroke of the tubular punch and prior to drawing of the sheetmetal.

10. The method of claim 9 in which the peripheral dimension of the sheetmetal blank is reduced in excess of twenty-five percent by the singledrawing stroke of the tubular punch.

11. The method of claim 10 in which the sheet metal blank comprisessteel.

References Cited UNITED STATES PATENTS Re. 20,009 6/ 1936 Hothersall72-351 1,453,652 5/1923 Auble et al. 72349 1,550,387 8/1925 Nilson et a172349 1,675,910 7/ 1928 Riker 72347 1,967,245 7/ 1934 Hothersall 7235 12,591,061 4/1952 Gaudreau 72351 3,203,218 8/1965 Bolt et al 72349FOREIGN PATENTS 280,900 5/ 1952 Switzerland.

CHARLES W. LANHAM, Primary Examiner E. M. COMBS, Assistant Examiner

